Gravity: String Theory

Introduction

There was hardly any time to wrestle with the implications of these ideas before yet another revolution in thinking hit the theoretical fan. In 1982, John Schwartz and Michael Green announced 'Superstring Theory'.

Henceforth, particles would not be thought of as point-like concentrations ofenergy, but as 1-D, vibrating 'strings' of energy.Particle world lines would be fattened from spaghetti-like, 1-D tracks in spacetime, to macaronni-like tubes, and with this new structure, all infinities would vanish without any need at allfor renormalization.

The only problem is that: 1) Spacetime would have to have either 10 or 26 dimensions in order that the theory was self-consistent; and 2) the theory would naturally work only at energies near 1019 GeV. The lowest "mode" of string oscillation would yield particles withno rest mass at all. The next-highest mass range would be 1019 GeV.

Throughout the 1980's and much of the 90's, string theorists have wrestled with forcing this "beautiful" theory to make predictions about particle physics in our low-energy world at the bottom of the energy ladder. Many feel that nature has been unkind to us by providing physicists with a 22nd Century theory, but only giving us 20th Century mathematics from which to crack openits secrets.

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Gravitational waves are propagating gravitational fields, "ripples" in the curvature of space-time, generated by the motion of massive particles, such as two stars or two black holes orbiting each other. Gravitational waves cause a variable strain of space-time, which result in changes in the distance between points, with the size of the changes proportional to the distance between the points. Gravitational waves can be detected by devices which measure the induced length changes. Waves of different frequencies are caused by different motions of mass, and difference in the phases of the waves allow us to perceive the direction to the source and the shape of the matter that generated them. (Source: NASA-The Laser Interferometer Space Antenna (LISA).)